1. Field of the Invention
The present invention relates to a method of designing rubber composite such as a pneumatic tire. More particularly, the present invention relates to a method of designing rubber composite in which, when designing rubber composite having high durability using the finite element method, a shape of the rubber composite, physical properties of a rubber material and physical properties of a reinforcement are efficiently selected, thus making it possible to obtain the durability as expected at the time of designing.
2. Description of the Related Art
In the method of designing the pneumatic tire or the like, it has been heretofore well known that a durability simulation is conducted by the use of the finite element method (hereinafter, abbreviated as FEM). The FEM has been established as a method for evaluating durability of a tire especially in designing a pneumatic tire for a heavy loading purpose used for a bus and a truck or in designing a pneumatic tire used for a light truck.
However, in the conventional method of designing a pneumatic tire using the FEM, simply air pressure and a rim were set to the pneumatic tire, and a desirable vertical load was applied thereto, followed by comparative review of magnitude of strain, stress or strain energy generated in each element. Thus, a shape of a tire, a shape of each part and physical properties of a rubber material were tentatively selected, and calculations using the FEM were repeated by trial and error based on the result of the tentative selections, whereby selecting the shape and the physical properties of the rubber material such that the strain, stress, and strain energy become relatively small.
However, according to the above-described method of designing, though it was expected that a defect would occur in a portion where the strain, the stress or the strain energy became the largest by the calculation, the defect sometimes occurred in a portion where the strain, the stress or the strain energy was calculated to be small in an actual durability test. Specifically, the actual result and the simulation result were not always consistent with each other.
For example, when principal strain of a belt edge cushion of a belt portion was 30% and principal strain of a carcass turnup around a bead portion was 20% as the FEM calculation result, according to the conventional notion, the belt edge cushion of the belt portion having larger principal strain was simply considered to be inferior to the carcass turnup around the bead portion in durability. However, actual tire durability was not consistent with such result in many cases.